It won't go away. Generations of scientists wrestle with it and it is one of the most compelling thought experiments. There are high estimates for the number of civilizations in the universe, but we don't see many of them. One should have arrived in the Solar System if the rapid expansion of civilizations were to occur in the Milky Way. It is implied that none exist.
Many people have tried to come up with a reason why we don't see any evidence of a technological civilization. It may be too difficult to travel through space. That could be it.
Our Solar System may not offer what long-lived, rapidly expanding civilizations want: the correct type of star.
The Drake Equation is needed to understand the Fermi Paradox. The Drake Equation estimates the number of civilizations in the universe. The concepts we have to wrestle with if we want to think about how many civilizations there could be are summarized in this document.
The Drake Equation is concerned with stars. The rate of star formation is one of the factors considered in the equation. How many of those planets develop life, how much of that life becomes technological civilization, and how many of those civilizations reveal their presence by releasing signals into space are some of the questions the Equation will ask. The life spans of those civilization are estimated.
Different estimates of how many technological civilizations there might be are given by using different variables. The thought experiment is informed by evidence.
The paper focuses on star types. Not all types of stars are good for a technological civilization. The best migration targets are low-mass stars.
The paper was accepted for publication by the Astrophysical Journal. Two authors are Jacob Haqq-Misra and Thomas Fauchez. At the Blue Marble Space Institute of Science, Haqq-Misra is a senior research investigator. Fauchez is a research assistant professor in physics at the American University.
The authors state that the absence of extraterrestrial settlement in the solar system means that expansionist civilizations do not exist.
The authors point to a famous analysis. Michael Hart was an American astronomer. The paper was published in the Quarterly Journal of the Royal Astronomical Society. It is believed to be the first thorough analysis of the paradoxes. In his paper, Hart showed how a civilization could expand quickly through the universe. If a civilization sent colonies to the nearest 100 stars, what would happen? They could colonize the star systems and each colony could do the same thing.
Hart wrote that if there was no pause between trips, the frontier of space exploration would be on the surface of a sphere. It would take 650,000 years for most of our galaxy to be traveled. Hart said that a technological civilization would have had enough time to reach us if they had started earlier. The only explanation for the lack of evidence is that there aren't any.
Hart concluded in his paper that SETI and similar efforts are a waste of time and money and that if anyone colonizes our Solar System, it will most likely be our descendants.
The authors don't agree.
Many people think that stars are attractive to a spacefaring civilization and that the civilization would spread everywhere. Is that correct?
The authors don't think so. They suggest that an expanding civilization will preferentially settle on low-mass K- or M-dwarf systems in order to maximize their longevity in the galaxy.
Humans don't like seeing stars by their longevity. What difference does it make if one type of star lasts 10 billion years and the other lasts 10 trillion? Imagine you are part of a body that makes decisions for a civilization that is a million years old or older. A star is important to you.
Red dwarfs and K dwarfs are long lived. It would take a lot of resources to colonize another solar system. Shouldn't those resources be used on a star system that may not last long?
If a civilization only focused on K dwarfs and M dwarfs, it would take a long time to colonize the universe. It would take two billion years to get to all low-mass stars. All M-dwarfs and all K-dwarfs would need about 0.2 ly and 0.2 ly, respectively, to be settled.
The time span could be reduced by two billion years. There could be even more expansion within 2 Myr with travel requirements of about 10 ly to settle all M-dwarfs and 50 ly to settle all K-dwarfs.
The estimates are based on a civilization moving through the universe. There would be times when the civ would be waiting for a favorable star to approach. The case can be made that civilizations can use close stellar encounters to expand quickly.
The 2 Myr settlement scenario is safe to reject, according to the authors. The assumption that the solar system has not been settled can be used to exclude this scenario. The low-mass star hypothesis is supported by the lack of evidence for any other civilization. Expansion of the solar system is limited to half the galaxy, M-dwarf stars, or K-dwarf stars.
We can't rule out the possibility of a low-mass star spreading through the Milky Way because we haven't seen it yet. The adage says that the absence of evidence isn't proof of absence. The G-dwarf system's low-mass Galactic Club would have had plenty of time to develop if we hadn't noticed it.
What drives a species to grow? Is population growth possible? Is there an energy need? Are there scientific curiosities? Do you think it's a case of dominion over others? They don't know much more about whether or not such expansion would be desirable for technological civilization in general.
There is no way we can know. Only 25% of a million years have passed since modern humans were first created. The first steps into space were made a few decades ago. The thought framework that guides us isn't time tested. The sociological structure of an ancient spacefaring species and if their drive to expand would continue is something we can't do much about. It might seem pointless after a while.
If we want to place more evidence-based constraints on our thinking, we need to look for signs of another civilization expanding. Our target should be low mass stars. The search for technosignatures in exoplanetary systems can help to place constraints on the existence of a low-mass Galactic Club. SETI and similar efforts are not a waste of time and resources according to them.
Our universe is governed by time. Time rules everything from our own lifespans to the ages of alien civilization. Time can be fiddled with, but it can't be stopped.
We don't know what kind of civilization there might be. We might be biased by our own experience. We are definitely. But what if alien life is not the same as ours? Is it possible that their experience of time is vastly different from ours?
Aliens can live so long that they can be part of multiple expansions into other star systems. Is it possible that they are a hybrid of an individual and genetic collective? They can take in new genetic information in ways we can't imagine. If breeding is outdated, and they are free from the concerns of a short life span, what would they do? If they are not organic anymore and the things that motivate us are in the past, what should we do? If they are symbionts, what do you think? There are a lot of what-ifs.
If their societies are different, there is no need to expand. Expansion might not be worth it. When the planet stops supporting life, it will doom civilization. Is it possible that they sidestep it somehow. But what if we can't think of anything else?
We can't think of things that aren't useless.
The end-point of many discussions is this. We can't comprehend that we don't know a lot. The toddler is humanity.
One of our most lovable qualities is our curious nature. The scientists like Haqq-Misra and Fauchez are interested in these topics. Is it true that they are correct? Is they right?
There is an expansion of a civilization in the sky.
It's possible that we never know. We should continue to look.
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